Linguistic and psychological theory coupled with empirical studies on the heritability of individual differences in language development and language disorders support the hypothesis that the capacity for language development in humans is genetically influenced. The proposed research will provide for further understanding of this genetic influence on language by studying individuals with specific language impairment (SLI) who have poor language development despite normal linguistic experience, sensory abilities, and nonverbal intelligence. Individuals with SLI provide an excellent means of identifying quantitative trait genetic loci that are likely to contribute to the full range of individual differences in language development and use. The proposed research will use two complementary strategies. First, it will take advantage of two individuals (TB) with severe developmental speech and language impairment, who also have a chromosomal translocation that appears to involve the FOXP2 gene. The FOXP2 gene is known to be a regulatory gene implicated in developmental speech and language disorder. This strategy will contrast the neuroanatomical, neurophysiological, and neuropsychological characteristics of these two individuals with their unaffected family members. This work will emphasize the procedural and declarative learning systems and vocabulary and sentence use. Thus, this strategy moves from gene to language phenotype to understand the neurologic and cognitive pathways between gene and phenotype. The second strategy will use a large epidemiologic sample of young adults with SLI along with their siblings who have participated in a 10-year longitudinal study. The language status, as well as associated conditions of these individuals, has been studied extensively. Furthermore, DNA samples have already been obtained from the SLI probands, siblings, and their parents. Thus, a valuable data bank of Doth tissue and phenotypes is available to identify genes by means of high density genome-wide screens using sib-pair linkage methods and follow-up fine mapping methods using transmission disequilibrium tests (TDT). Additionally, ongoing fine mapping of candidate genes and regions of interest informed by findings from our laboratories and other laboratories will be carried out along with microdeletion studies. Additional phenotyping of the SLI probands and siblings will be conducted to obtain procedural and declarative learning measures and additional language measures that parallel the data to be obtained from the TB family. The learning measures are to serve as endophyenotypes that may be more sensitive and specific to genetic influence. The phenotypes and endophenotypes from these individuals will then be used in conjunction with the existing genotyping for additional genome-wide screens and further follow-up fine mapping studies.